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Title: Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology
Author: P. von Paris, A. Petau, J.L. Grenfell, E. Hauber, D. Breuer, R. Jaumann, H. Rauer, D. Tirsch

We compare estimates of atmospheric precipitation during the Martian Noachian-Hesperian boundary 3.8 Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2-H2O-N2 atmospheres with surface pressures varying from 20 mb to 3 bar with input solar luminosity reduced to 75% the modern value.
Results from the valley network analysis are of the order of a few mm d-1 liquid water precipitation (1.5-10.6 mm d-1, with a median of 3.1 mm d-1). Atmospheric model results are much lower, from about 0.001-1 mm d-1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favour a cold early Mars with episodic snowmelt as a source for runoff.
Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity- which affect the atmospheric result - as as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.

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Radar Map of Buried Martian Ice Adds to Climate Record

Extensive radar mapping of the middle-latitude region of northern Mars shows that thick masses of buried ice are quite common beneath protective coverings of rubble.
The ability of NASA's Mars Reconnaissance Orbiter to continue charting the locations of these hidden glaciers and ice-filled valleys -- first confirmed by radar two years ago -- adds clues about how these deposits may have been left as remnants when regional ice sheets retreated.
The subsurface ice deposits extend for hundreds of kilometres in the rugged region called Deuteronilus Mensae, about halfway from the equator to the Martian north pole. Jeffrey Plaut of NASA's Jet Propulsion Laboratory, Pasadena, California, and colleagues prepared a map of the region's confirmed ice for presentation at this week's 41st Lunar and Planetary Science Conference near Houston.

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Credit:    NASA/JPL-Caltech/ASI/University of Rome/Southwest


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Spectacular satellite images suggest that Mars was warm enough to sustain lakes 3 billion years ago, a period that was previously thought to be too cold and arid to sustain water on the surface, according to research published today in Geology.
The research, by a team from Imperial College London and UCL, suggests that during the Hesperian Epoch, approximately 3 billion years ago, Mars had lakes made of melted ice, each around 20km wide, along parts of the equator.

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New images of Mars suggest the Red Planet had large lakes on its surface as recently as three billion years ago.
The evidence comes from Nasa's Mars Reconnaissance Orbiter (MRO) which spied a series of depressions linked by what look like drainage channels.
Scientists tell the journal Geology that the features bear the hallmarks of being produced by liquid water.

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Trough Deposits on Mars Point to Complex Hydrologic Past

Catherine Weitz, a senior scientist at the Tucson-based Planetary Science Institute, has reported new evidence for multiple, water-related geologic processes on Mars.
She and her colleagues studied light-toned deposits (LTDs) within troughs of the Noctis Labyrinthus region in western Valles Marineris using data gathered by three Mars Reconnaissance Orbiter (MRO) instruments: the High Resolution Imaging Science Experiment (HiRISE) camera, the Context Camera (CTX) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).
Weitz presented the research results today during a morning session of the American Geophysical Union Conference in San Francisco, California.

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Mars may have once hosted a body of water roughly the size of Lake Michigan, say researchers who have found a telltale "bathtub ring" of minerals inside an ancient Martian impact crater.
The find means that Columbus crater, in Mars's southern hemisphere, is the best place yet to study the chemistry of so-called fossil lakes on the red planet, the scientists say.

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A single ocean once covered much of the northern half of Mars, supplied with water from a belt of rain-fed rivers, new research suggests.
Scientists have produced a map showing that Martian valley networks are more than twice as extensive as had previously been thought, indicating that they were carved by rivers.

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The red lines marked show where scientists believe valleys were formed by a network of rivers feeding into the ocean. The area is twice as extensive than that mapped by earlier research (the blue lines).

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This global map shows the ocean (in  blue) and the location of the valleys (in yellow, red and green) which are believed to have formed by water flowing from the south towards the northern ocean.

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A new detailed map of Mars shows what was likely a vast ocean in the north and valleys around the equator, suggesting that the planet once had a humid, rainy climate, according to research published Monday.
The computer-generated map, based on topographic data from NASA satellites, also shows that the network of valleys on the red planet is at least twice as extensive as previously estimated.

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Meteorite impacts turn up nearly pure water ice in Mars's mid-latitudes
Planetary scientists looking for water ice on Mars have employed a number of tactics to great success in their search. The Phoenix lander dug it up; orbiting radar measurements have seen it under insulating blankets of debris. (Frozen water sublimates to vapour in Mars's climate and so is not stable when exposed at the surface.)

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How Martian clouds create snowfall
The planet Mars conjures images of red rocks and arid, dusty plains, but as NASA's Phoenix Mars Lander showed last year, it snows on Mars.
The stationary robot observed ice crystals falling to the Martian surface near the end of its five-month mission in the arctic Vastitas Borealis plains last year. Scientists provided further details on this finding and others in a set of four papers in Friday's issue of the journal Science. The research could help shed light on the past and present action of water on the Martian surface and characterize the potential habitability of the Red Planet.

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